Method of and apparatus for producing metallic articles by electroslag melting

ABSTRACT

A method of producing a metallic article by feeding consumable electrodes consisting of a suitable metallic material continuously at a predetermined rate of speed into a slag bath formed in a water-cooled metal mould defining a moulding cavity of the same cross-sectional shape as that of the desired metallic article, successively solidifying in said water-cooled metal mould the molten metal formed continuously by the electroslag melting of said consumable electrodes and continuously withdrawing said solidified metal from said mould at a predetermined rate of speed, characterized in that the consumable electrodes preferably have a transverse cross-sectional area larger than that of the desired metallic article are used, and the slag bath and the molten metal in the water-cooled metal mould are heated by non-consumable electrodes.

United States Patent METHOD OF AND APPARATUS FOR PRODUCING METALLIC ARTICLES BY ELECTROSLAG MELTING [75] Inventor: Akira Ujiie, Kobe, Japan [73] Assignee: Mitsubishi Jukogyo Kabushiki Kaisha, Tokyo, Japan [22] Filed: July 27, 1973 [21] Appl. No.: 383,057

[30] Foreign Application Priority Data Aug. 28, 1972 Japan 47-85294 [52] US. Cl 164/52; 164/252 [51] Int. Cl. B22D 27/02 [58] Field of Search 164/52, 252

[56] References Cited UNITED STATES PATENTS 2,191,480 2/1940 Hopkins 164/252 3,571,475 3/1971 Holzgruber et al. 164/52 X 3,650,311 3/1972 Fritsche 164/52 3,677,323 7/1972 Wahlster et al. 164/52 3,683,997 8/1972 Uziie et al....... 164/52 3,767,831 10/1973 Plockinger et al 164/52 X OTHER PUBLICATIONS Medovar et al., Electroslag Remelting, JPRS 22217,1963, copy in group 322, pp. 159-161.

Primary Examiner-Robert D. Baldwin Assistant ExaminerJohn E. Roethel Attorney, Agent, or Firm-Cushman, Darby and Cushman [57] ABSTRACT A method of producing a metallic article by feeding consumable electrodes consisting of a suitable metallic material continuously at a predetermined rate of speed into a slag bath formed in a water-cooled metal mould defining a moulding cavity of the same crosssectional shape as that of the desired metallic article, successively solidifying in said water-cooled metal mould the molten metal formed continuously by the electroslag melting of said consumable electrodes and continuously withdrawing said solidified metal from said mould at a predetermined rate of speed, characterized in that the consumable electrodes preferably have a transverse cross-sectional area larger than that of the desired metallic article are used, and the slag bath and the molten metal in the water-cooled metal mould are heated by non-consumable electrodes.

13 Claims, 4 Drawing Figures US. Patent Nov. 25, 1975 Sheetlof3 3,921,699

US. Patent Nov. 25, 1975 Sheet20f3 3,921,699

US. Patent Nov. 25, 1975 Sheet3of3 3,921,699

METHOD OF AND APPARATUS FOR PRODUCING METALLIC ARTICLES BY ELECTROSLAG MELTING BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to improvements in the method of producing hollow metallic articles, such as tubes, pipes, bodies of pressure containers, spherical containers and bent tubes, and solid metallic articles having optional transverse cross-sectional shapes, from molten metals obtained by melting consumable electrodes of the desired metallic materials in a slag bath by electroslag melting.

2. Description of the Prior Art Metallic articles of the types described above have,

heretofore been produced by a FIG. 1 type method comprising arranging consumable electrodes e in a shape corresponding to the transverse cross-sectional shape of a metallic article in desired to be produced, each of said consumable electrodes having a thickness 1 as shown in FIG. 1 relative to the wall thickness T of the metallic article in and a transverse cross-sectional shape substantially the same as that of said metallic article, and melting said consumable electrodes e in a slag bath S of relatively small volume by electroslag melting, as illustrated in FIG. 1. Therefore, there have been the problems that the rate of formation of the molten metal is very low and the rate of cooling of the same is also relatively low, and that accordingly there is the strong tendency for the dendritic structure D of the metallic article 111 to become coarse and the sizes of the metal grains thereof become relatively large. In addition, the conventional method has had the disadvantage that the production of the consumable electrodes is cumbersome and is difficult particularly when the metallic article 111 is small in thickness, because the consumable electrodes must be made for each metallic article desired to be produced in a transverse cross-sectional shape and dimensions matching with those of the particular metallic article.

SUMMARY OF THE INVENTION The present invention is proposed with a view to providing a method of producing metallic articles by electroslag melting, which is free of the above-described problems and disadvantage of the prior art method and in which the rate of formation and rate of cooling of molten metal are increased to provide for the production of quality metallic articles having fine grain structure. Namely, the present invention includes a method of producing a metallic article by feeding consumable electrodes consisting of a suitable metallic material continuously at a predetermined rate of speed into a slag bath formed in a water-cooled metal mould defining a moulding cavity of the same cross-sectional shape as that of the desired metallic article, successively solidifying in said water-cooled metal mould the molten metal formed continuously by the electroslag melting of said consumable electrodes and continuously withdrawing said solidified metal from said mould at a predetermined rate of speed, characterized in that consumable electrodes preferably having a transverse cross-sectional area larger than that of the desired metallic article are used. and the slag bath and the molten metal in the water-cooled metal mould are heated by non-consumable electrodes.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a diagram briefly illustrating a prior art method;

FIG. 2 is a vertical cross-sectional view showing briefly one form of the apparatus for practicing the method of the present invention;

FIG. 3 is a transverse cross-sectional view of the apparatus of FIG. 2 in which a plurality of pairs of consumable electrodes are arranged in adjacent relation; and

FIG. 4 is a vertical cross-sectional view of another form of the apparatus for practicing the method of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The method of the invention will be described practically hereunder with reference to FIGS. 2 and 3 which show an apparatus designed for producing a tubular metallic article according to the method of this invention.

Referring first to FIG. 2, reference numeral 1 designates consumable electrodes consisting of a suitable metallic material. The consumable electrodes are made in a thickness 2 considerably larger than the wall thickness T of a tubular metallic article M desired to be produced. A plurality (16 in the apparatus shown) of the consumable electrodes 1 are arranged in adjacent relation circumferentially in a shape corresponding to the transverse cross-sectional shape of the tubular metallic article M, as shown in FIG. 3, and are continuously moved downwardly at a predetermined rate of speed by feed means not shown. Reference numeral 2 designates an annular wateracooled metal mould consisting of a water-cooled outer mould unit 20 and a water-cooled inner mould unit 2b arranged concentrically and defining therebetween an annular moulding cavity which is made up of an upper section, a central parallel section and a lower section. The central parallel section of the moulding cavity has a transverse cross-sectional shape same as that of the tubular metallic article M and a width equal to the wall thickness T of said metallic article, and its vertical length is longer than in the conventional apparatus shown in FIG. 1. The upper section of the moulding cavity is expanded upwardly and is formed with a step at the portion adjoining the central parallel portion, and the portion of said upper section above said step constitutes a slag bath receiving portion 3 and the portion of the same below said step constitutes a portion for accommodating a molten metal pool 4. Each of the consumable electrodes 1 is arranged to be submerged at its lower end into the central portion of a slag bath S filled in the slag bath receiving portion 3. Reference numeral 5 designates non-consumable electrodes. These non-consumable electrodes 5 are arranged on one or both sides of each consumable electrode 1 in adjacent relation thereto, with their lower end portions submerged deeply into the slag bath S in the slag bath receiving portion 3. These non-consumable electrodes 5 serve to heat the slag bath S and the molten metal in the molten metal pool 4 to prevent cooling of them and to alleviate the cooling action of the water-cooled metal mould 2 on said molten metal, and their lower ends are positioned close to the molten metal pool 4.

An arrangement may be made to cause each nonconsumable electrode 5 to make a horizontal movement or oscillation circumferentially (as diagrammatically shown for one electrode 5 by arrow A in FIG, 3) in the slag bath 5 either alone or along with the associated consumable electrode 1. Such arrangement is advantageous in heating the slag bath S and molten metal more uniformly by the non-consumable electrodes. Reference numeral 6 designates a start piece fixed to article withdrawing means 7 provided beneath the water-cooled metal mould 2. The start piece 6 is formed such that its upper end portion can move into the central parallel section of the moulding cavity of the metal mould 2 and its top end face can close the upper open end of said central parallel section. The article with-. drawing means 7 is moved up and down at a predetermined rate of speed by driving means not shown. Reference numeral 8 designates a power source connected with each consumable electrode 1 and the start piece 6, 9 a power source connected with each non-consumable electrode 5 and the start piece 6, and 10 a slag film formed on each of the inner and outer surfaces of the tubular metallic article M.

In the operation, the article withdrawing means 7 is elevated to insert the start piece 6 into the central parallel section of the moulding cavity of the water-cooled metal mould 2 from the underside and to close the upper open end of said central parallel section by the upper end face of said start piece 6. Thereafter, the consumable electrodes 1 are moved downwardly to locate the lower ends thereof within the upper section of the moulding cavity and a molten slag prepared separately is poured into the slag bath receiving portion 3 to form the slag bath S. In this case, the lower end portion of each consumable electrode 1 is submerged in the slag bath S and the lower end portion of each non-consumable electrode 5 is also submerged deep in said slag bath as it is previously positioned deep in the upper section of the moulding cavity. Then, the power source 8 is closed to conduct a current across the start piece 6 and each consumable electrode 1, and each consumable electrode 1 is moved down atthe predetermined rate of speed. Each consumable electrode 1 is melted from its lower end by electroslag melting and the resultant droplets la of molten metal successively fall in the slag bath S and accumulate in the molten metal accommodating portion of the upper section of the moulding cavity to form a molten metal pool 4. The power source 9 is closed substantially concurrently to conduct a current from each non-consumable electrode 5 to the molten metal at through the slag bath 5 and to heat said slag bath and molten metal by said non-consumable electrodes. The molten metal m tends to cool rapidly by being cooled by the water-cooled metal mould 2 but, on the, other hand, said molten metal In and the slag bath 5 are heated by the nonconsumable electrodes 5 as stated above. Consequently, the cooling rate of the molten metal is reduced and the molten metal at remains in the molten state within the molten metal pool 4, without cooling and solidifying rapidly from the portion in contact with the metal mould 2 as is in the prior art method, and bonds with the top end face of the start piece 6 at its lower end. When the article withdrawing means 7 is lowered at the predetermined rate of speed thereafter, the molten metal m moves down through the parallel section ofthe moulding cavity at the same rate of speed. during which period it is cooled from the inside and outside by the water-cooled metal mould 2 and solidified successively. Thus, a solidified metal having the predetermined 4 thickness T or the desired tubular metallic article M is produced. The article M is successively withdrawn from the metal mould 2 by the withdrawing means 7, at the predetermined rate of speed. Since the thickness t of the consumable electrodes 1 is considerably larger than the width T of the central parallel section of the moulding cavity, the droplets 1a of molten metal are formed at a higher rate and accordingly a larger amount of the molten metal In accumulates in the molten metal pool 4 in a unit time. However, that larger amount of molten metal In remains in a flowable state by being heated by the non-consumable electrodes 5 to reduce the cooling rate, all as stated above and, therefore, that larger amount of molten metal moves smoothly downwardly into the central parallel section of the moulding cavity as the start piece 6 moves down. Further, the amount of the molten metal In movable downwardly from pool 4 in a unit time is so large that the rate of withdrawal of the molten metal In by the withdrawing means 7 can be increased, and cooling of the metallic article M can be achieved sufficiently as the central parallel section of the moulding cavity has a vertical length longer than in the prior art apparatus.

In the prior art method, the consumable electrodes r are generally submerged shallowly in the slag bath and the electroslag melting of said electrodes takes place at a portion of the slag bath close to the surface thereof,

as shown in FIG. 1.,Therefore, the temperature of the slag bath is relatively high at the upper portion and rel atively low at the bottom portion thereof and convection of the slag within the slag bath occurs only insufficiently. In the present invention, however, the nonconsumable electrodes 5 are used as auxiliary heating sources and their lower ends can be moved closely. to

the molten metal pool 4. Therefore, the temperature of i This is because, if the current is passed only across the consumable electrodes and the molten metal, the temperature of the molten metal would rise and the depth of the molten metal pool would increase, but since the rate of formation of the molten metal droplets per unit time is constant, the heat of the molten metal would be useful only for maintaining the molten metal in a flowable state and not for increasing the supply of molten metal droplets, and it would be impossible to increase the molten metal withdrawing rate, with the consequence that the depth of the molten metal pool becomes excessively large and the molten metal being withdrawn is not solidified sufficiently only by the cooling effect of the water-cooled metal mould, and finally the metal emerges from the lower section of the moulding cavity as being melted. It is for this reason why in the prior art method the current has been passed across the respective consumable electrodes to increase the rate of formation of molten metal droplets and has i been passed slightly to the molten metal pool. In this case, however. since the current tends to pass in the surface layer of the slag bath where the temperature and electric conductivity are relatively high, it is impossible to submerge the consumable electrodes deep into the slag bath. In the prior art method, therefore, the slag bath is formed in a relatively small depth and accordingly the amount of slag is small and the thermal inertia thereof is small, so that a powdered flux is usually supplied to replenish the slag. However, the flux takes much time before it is converted into slag and has detrimental effects of lowering the slag bath temperature and impairing the flowability of the slag. According to the method of this invention, as stated previously, the slag bath is maintained at a uniform temperature and its lower portion has a high temperature and good electric conductivity, so that the consumable electrodes 1 can be penetrated deep into the slag bath S and sufficient current can be easily conducted across the respective consumable electrodes 1 and concurrently, across the consumable electrodes and the mo]- ten metal In. The depth of the slag bath S can also be made large, so that the powdered flux can be supplied without lowering the temperature of the slag bath S or impairing the flowability of the same, and stable electroslag melting can be obtained. Since the molten metal droplets can be supplied sufficiently to the molten metal pool 4, the withdrawing rate of the article withdrawing means 7 can be increased remarkably as compared with that in the prior art method and in no case will the depth of the molten metal pool become excessively large. Therefore, the molten metal being withdrawn is sufficiently cooled and solidified by the watercooled metal mould to give the desired article M and there is no fear of the molten metal emerging from the metal mould in the molten state. The slag bath S has a uniform temperature distribution, and is high in temperature and freely flowable. Therefore, slag films 10 formed between the water-cooled metal mould.2, and the molten metal in and the tubular article being produced, are very thin and attach uniformly to the inner and outer surfaces of the tubular article M, thus giving a beautiful appearance to the surfaces of and increasing the dimensional accuracy of the product tubular article M.

As may be clearly understood from the foregoing description, the method of the invention of producing a metallic article by feeding consumable electrodes consisting of a suitable metallic material continuously at a predetermined rate of speed into a slag bath formed in a water-cooled metal mould defining a moulding cavity of the same cross-sectional shape as that of the desired metallic article, successively solidifying in said watercooled metal mould the molten metal formed continuously by the electroslag melting of said consumable electrodes and continuously withdrawing said solidified metal from said mould at a predetermined rate of speed, is characterized by using consumable electrodes of a transverse cross-section larger than that of the desired metallic article and heating the slag bath and the molten metal in the metal mould by non-consumable electrodes. Therefore, according to the method of the invention, the following practical advantages can be achieved:

1. By using the nonconsumable electrodes as auxiliary heating sources, one or a plurality of consumable electrodes having a total transverse cross-sectional area larger than the transverse cross-sectional area of a metallic article desired to be produced can be melted at a high rate by electroslag melting and the rate of withdrawal of the metallic article or the article production rate can be increased accordingly as compared with that in the prior art method. The molten metal cooling rate can also be increased, so that the dendritical structure of the metallic article does not grow so extensively as in metallic articles produced by the prior art method and the grain size is small. Therefore, the metallic article produced by the method of this invention has a remarkably improved quality over the articles produced by the prior art method.

2. It is unnecessary to produce consumable electrodes of specific dimensions for the production of a particular article, even when the wall thickness of the article is small.

3. Since the temperature of the slag bath is high and sufficient convection of the slag takes place in said slag bath, the impurities can be removed sufficiently and sufficient smelting of the molten metal can be attained. In addition, since the molten slag in the slag bath is cooled by the water-cooled metal mould and shields the inner and outer surface of the metallic article in the form of a thin film, the surface appearance of the metallic article is improved and the dimensional accuracy thereof increases.

4. The volume of the slag bath can be increased and, therefore, the electroslag melting can be achieved with stability and the production operation can be carried out smoothly.

In FIG. 4 is shown another form of the apparatus for practicing the method of this invention, in which pocket grooves 11 are respectively formed in the outer mould unit 2a and inner mould unit 2b of the watercooled metal mould 2 for accumulating therein impurities 12 which are not floatable. The apparatus of this form is advantageous in that the purity of the molten metal m can be maintained high and that the temperature thereof can be maintained at a higher level since the cooling effect of the metal mould 2 on the molten metal is moderated by the pocket grooves 11.

I claim:

1. In an electroslagmelting method for producing a metallic article using a liquid cooled metal mould with inner and outer spaced parts and upper, central and lower sections with the facing sides of the central sections being parallel spaced the thickness of said article and that spacing being of the same cross-sectional shape as that of said metallic article, and with at least one of said upper sections having its inner side sloping outwardly away from the other side a significant angle relative to the vertical to form a slag receiving trough with a bottom well atop the open upper end of the space between said central parallel sections, the improvement comprising the steps of:

inserting a start piece upwardly into the space between the central parallel sections to close the said upper open end of said space,

disposing at least one nonconsumable electrode substantially at said angle into said trough adjacent at least said one side thereof and deeply thereinto so that the bottom end of each said electrode is adjacent the said well,

disposing molten slag into said trough to form a slag bath,

feeding at least one consumable electrode continuously at a predetermined rate of speed deeply into said slag bath to cause electroslag melting of the lower end of said consumable electrode with the resultant droplets of molten metal successively falling in the slag bath and accumulating in a molten metal pool in said well,

heating said molten metal pool by said non-consumable electrode to cause bonding of molten metal from said pool to the top end face of said start piece and to cause a substantially uniform temperature distribution in said slag bath to reduce the cooling rate of the molten metal pool which would otherwise be more quickly cooled by said liquid cooled mould and therefore less rapidly movable downwardly from said well through said space between said central parallel sections, withdrawing said start piece downwardly through the said space between said parallel central sections of said mould to cause molten metal from said heated pool to move continuously downward therewith at the same rate of speed which is greater than if said molten metal pool heating had not occurred. and

cooling said molten metal and successively solidifying same as it moves downwardly between said central parallel sections for producing at the lower section of said mould a continuous solidified metallic article with reduced growth of dendritical structure and with a smaller grain size due to said pool heat ing.

2. A method as in claim 1 including further reducing the mould cooling effect on said molten metal pool by at least one pocket alongside said pool and accumulating non-floatable impurities in said pocket,

3. In an electroslag melting method for producing a hollow metallic article the improvement comprising the steps of:

providing a liquid cooled metal mould with inner and outer spaced parts and upper, central and lower sections with the facing sides of the central sections being parallel spaced the thickness of the side of said hollow article and that spacing being of the same cross-sectional shape as that of said metallic article, and with said upper sections having their inner sides sloping outwardly away from each other a significant angle to form a slag receiving trough with a central bottom well atop the open upper end of the space between said central parallel sections,

inserting a start piece upwardly into the space between the central parallel sections to close the said upper open end of said space,

disposing non-consumable electrodes substantially at said angle into said trough at spaced points therealong adjacent said sides thereof and deeply thereinto so that the bottom ends of said electrodes are adjacent the said well,

disposing molten slag into said trough to form a slag bath,

feeding consumable electrodes, which have a thickness greater than said central spacing thickness, continuously at a predetermined rate of speed deeply into said slag bath at said spaced points to cause electroslag melting of the lower ends of said consumable electrodes with the resultant droplets of molten metal successively falling in the slag bath and accumulating in a molten metal pool in said well,

heating said molten metal pool by said non-consumable electrodes to cause bonding of molten metal from said pool to the top end face of said start piece and to cause a substantially uniform temperature distribution in said slag bath to reduce the cooling rate of the molten metal pool which would otherwise be more quickly cooled by said liquid cooled mould and therefore less rapidly movable downwardly from said well through said space between said parallel sections,

withdrawing said start piece downwardly through the said space between said parallel central sections of said mould to cause molten metal from said heated pool to move continuously downward therewith at the same rate of speed which is greater than if said the cooling effect of said mould on said molten metal 7 pool by grooves in the bottom of said trough on both sides of said well and accumulating non-floatable impurities in said grooves. i

5. A method as in claim 3 including moving at least one of the said electrodes in said slag bath to cause said heating of said molten metal pool and slag bath to be even more uniform.

6. Apparatus for producing a desired metallic article comprising: i

a liquid cooled metal mould having two vertically disposed spaced parts each of which has upper, central and lower sections with the central sections having facing inner parallel sides spaced the thickness of said article and with that spacing being of the same cross-sectional shape as that of said article,

at least one of said upper sections having its inner side upwardly sloping outwardly a significant angle relative to the vertical to form with the inner side of the other upper section a slag receiving trough hava ing a bottom well atop the open upper end of the space between said central section facing sides for receiving molten slag,

a start piece,

means for moving said start piece upwardly into the said space between the central parallel facing sides to close the upper open end of said space for ini-' tially forming the bottom of said well,

at least one non-consumable electrode disposed sub-' stantially at said angle into said trough adjacent at least said one sloping side thereof and deeply thereinto so that the bottom end of each said non-consumable electrode is adjacent said well,

means for feeding at least one consumable electrode continuously at a predetermined rate of speed deeply into said trough,

means for electroslag melting of the lower end of said consumable electrode for causing droplets of molten metal to fall successively into said slag bath and accumulate in a molten metal pool in said well,

means including each said non-consumable electrode for heating said molten metal pool to cause bond ing of molten metal from said pool to the topend face of said start piece and to cause a substantially uniform temperature distribution in said slag bath to reduce the cooling rate of the molten metal pool,

which would otherwise be more quickly cooled by said liquid cooled mould and therefore less rapidly movable downwardly from said well through said space between said central section parallel facing sides, 9

said start piece upwardly moving means including means for withdrawing said start piece downwardly through said space between said parallel facing sides of said central sections of said mould to cause molten metal from said heated pool to move continuously downward therewith at the same rate of speed which is greater than if said molten metal pool heating had not occurred, and

said liquid cooled metal mould including central and lower section cooling means for cooling said molten metal and successively solidifying same as it moves downwardly between said central section parallel faces for producing at the lower section of said mould a continuous solidified metallic article with reduced growth of dendritical structure and with a smaller grain size due to said pool heating.

7. Apparatus as in claim 6 wherein each said consumable electrode has a transverse cross-sectional area larger than that of the said desired metallic article.

8. Apparatus as in claim 6 including means for moving at least said non-consumable electrode in said trough for causing said heating of said molten metal pool and slag bath to be more uniform.

9. Apparatus as in claim 6 including means for moving said consumable and non-consumable electrodes in said trough and in addition to said feeding of said consumable electrode for more uniformly heating said molten metal pool and slag bath.

10. Apparatus as in claim 6 including pocket means alongside said well for accumulating non-floatable impurities.

11. Apparatus as in claim 6 wherein the inner side of said other upper section upwardly slopes outwardly at substantially said significant angle relative to the vertical and wherein there is at least one other nonconsumable electrode disposed at said angle into said trough adjacent said sloping inner side of said other upper section and deeply into said trough so that the bottom end of each said other non-consumable electrode is adjacent said well, said heating means being operable also to heat each said other non-consumable electrode.

12. Apparatus as in claim 6 wherein said desired metallic article is hollow and has a predetermined transverse cross-sectional shape,

said liquid cooled metal mould, trough, start piece and spacing between said central section parallel facing sides being of the same cross-sectional shape as said desired metallic article,

there being a multiplicity of said consumable electrodes continuously fed by said feeding means at said predetermined rate of speed deeply into said trough and melted as aforesaid by said electroslag melting means for adding further droplets of molten metal into said molten metal pool.

13. Apparatus as in claim 12 wherein said multiplicity of consumable electrodes are disposed in pairs at successive points along said trough, there being a pair of said nonconsumable electrodes adjacent each said pair of consumable electrodes. 

1. In an electroslag melting method for producing a metallic article using a liquid cooled metal mould with inner and outer spaced parts and upper, central and lower sections with the facing sides of the central sections being parallel spaced the thickness of said article and that spacing being of the same cross-sectional shape as that of said metallic article, and with at least one of said upper sections having its inner side sloping outwardly away from the other side a significant angle relative to the vertical to form a slag receiving trough with a bottom well atop the open upper end of the space between said central parallel sections, the improvement comprising the steps of: inserting a start piece upwardly into the space between the central parallel sections to close the said upper open end of said space, disposing at least one non-consumable electrode substantially at said angle into said trough adjacent at least said one side thereof and deeply thereinto so that the bottom end of each said electrode is adjacent the said well, disposing molten slag into said trough to form a slag bath, feeding at least one consumable electrode continuously at a predetermined rate of speed deeply into said slag bath to cause electroslag melting of the lower end of said consumable electrode with the resultant droplets of molten metal successively falling in the slag bath and accumulating in a molten metal pool in said well, heating said molten metal pool by said non-consumable electrode to cause bonding of molten metal from said pool to the top end face of said start piece and to cause a substantially uniform temperature distribution in said slag bath to reduce the cooling rate of the molten metal pool which would otherwise be more quickly cooled by said liquid cooled mould and therefore less rapidly movable downwardly from said well through said space between said central parallel sections, withdrawing said start piece downwardly through the said space between said parallel central sections of said mould to cause molten metal from said heated pool to move continuously downward therewith at the same rate of speed which is greater than if said molten metal pool heating had not occurred, and cooling said molten metal and successively solidifying same as it moves downwardly between said central parallel sections for producing at the lower section of said mould a continuous solidified metallic article with reduced growth of dendritical structure and with a smaller grain size due to said pool heating.
 2. A method as in claim 1 including further reducing the mould cooling effect on said molten metal pool by at least one pocket alongside said pool and accumulating non-floatable impurities in said pocket.
 3. In an electroslag melting method for producing a hollow metallic article the improvement comprising the steps of: providing a liquid cooled metal mould with inner and outer spaced parts and upper, central and lower sections with the facing sides of the central sections being parallel spaced the thickness of the side of said hollow article And that spacing being of the same cross-sectional shape as that of said metallic article, and with said upper sections having their inner sides sloping outwardly away from each other a significant angle to form a slag receiving trough with a central bottom well atop the open upper end of the space between said central parallel sections, inserting a start piece upwardly into the space between the central parallel sections to close the said upper open end of said space, disposing non-consumable electrodes substantially at said angle into said trough at spaced points therealong adjacent said sides thereof and deeply thereinto so that the bottom ends of said electrodes are adjacent the said well, disposing molten slag into said trough to form a slag bath, feeding consumable electrodes, which have a thickness greater than said central spacing thickness, continuously at a predetermined rate of speed deeply into said slag bath at said spaced points to cause electroslag melting of the lower ends of said consumable electrodes with the resultant droplets of molten metal successively falling in the slag bath and accumulating in a molten metal pool in said well, heating said molten metal pool by said non-consumable electrodes to cause bonding of molten metal from said pool to the top end face of said start piece and to cause a substantially uniform temperature distribution in said slag bath to reduce the cooling rate of the molten metal pool which would otherwise be more quickly cooled by said liquid cooled mould and therefore less rapidly movable downwardly from said well through said space between said parallel sections, withdrawing said start piece downwardly through the said space between said parallel central sections of said mould to cause molten metal from said heated pool to move continuously downward therewith at the same rate of speed which is greater than if said molten metal pool heating had not occurred, and cooling said molten metal from both sides and successively solidifying same as it moves downwardly between said central parallel sections for producing at the lower section of said mould a continuous solidified hollow metallic article with reduced growth of dendritical structure and with a smaller grain size due to said pool heating.
 4. A method as in claim 3 including further reducing the cooling effect of said mould on said molten metal pool by grooves in the bottom of said trough on both sides of said well and accumulating non-floatable impurities in said grooves.
 5. A method as in claim 3 including moving at least one of the said electrodes in said slag bath to cause said heating of said molten metal pool and slag bath to be even more uniform.
 6. Apparatus for producing a desired metallic article comprising: a liquid cooled metal mould having two vertically disposed spaced parts each of which has upper, central and lower sections with the central sections having facing inner parallel sides spaced the thickness of said article and with that spacing being of the same cross-sectional shape as that of said article, at least one of said upper sections having its inner side upwardly sloping outwardly a significant angle relative to the vertical to form with the inner side of the other upper section a slag receiving trough having a bottom well atop the open upper end of the space between said central section facing sides for receiving molten slag, a start piece, means for moving said start piece upwardly into the said space between the central parallel facing sides to close the upper open end of said space for initially forming the bottom of said well, at least one non-consumable electrode disposed substantially at said angle into said trough adjacent at least said one sloping side thereof and deeply thereinto so that the bottom end of each said non-consumable electrode is adjacent said well, means for feeding at least one consumable electrode continuously at a predetermined rate of speed deePly into said trough, means for electroslag melting of the lower end of said consumable electrode for causing droplets of molten metal to fall successively into said slag bath and accumulate in a molten metal pool in said well, means including each said non-consumable electrode for heating said molten metal pool to cause bonding of molten metal from said pool to the top end face of said start piece and to cause a substantially uniform temperature distribution in said slag bath to reduce the cooling rate of the molten metal pool which would otherwise be more quickly cooled by said liquid cooled mould and therefore less rapidly movable downwardly from said well through said space between said central section parallel facing sides, said start piece upwardly moving means including means for withdrawing said start piece downwardly through said space between said parallel facing sides of said central sections of said mould to cause molten metal from said heated pool to move continuously downward therewith at the same rate of speed which is greater than if said molten metal pool heating had not occurred, and said liquid cooled metal mould including central and lower section cooling means for cooling said molten metal and successively solidifying same as it moves downwardly between said central section parallel faces for producing at the lower section of said mould a continuous solidified metallic article with reduced growth of dendritical structure and with a smaller grain size due to said pool heating.
 7. Apparatus as in claim 6 wherein each said consumable electrode has a transverse cross-sectional area larger than that of the said desired metallic article.
 8. Apparatus as in claim 6 including means for moving at least said non-consumable electrode in said trough for causing said heating of said molten metal pool and slag bath to be more uniform.
 9. Apparatus as in claim 6 including means for moving said consumable and non-consumable electrodes in said trough and in addition to said feeding of said consumable electrode for more uniformly heating said molten metal pool and slag bath.
 10. Apparatus as in claim 6 including pocket means alongside said well for accumulating non-floatable impurities.
 11. Apparatus as in claim 6 wherein the inner side of said other upper section upwardly slopes outwardly at substantially said significant angle relative to the vertical and wherein there is at least one other nonconsumable electrode disposed at said angle into said trough adjacent said sloping inner side of said other upper section and deeply into said trough so that the bottom end of each said other non-consumable electrode is adjacent said well, said heating means being operable also to heat each said other non-consumable electrode.
 12. Apparatus as in claim 6 wherein said desired metallic article is hollow and has a predetermined transverse cross-sectional shape, said liquid cooled metal mould, trough, start piece and spacing between said central section parallel facing sides being of the same cross-sectional shape as said desired metallic article, there being a multiplicity of said consumable electrodes continuously fed by said feeding means at said predetermined rate of speed deeply into said trough and melted as aforesaid by said electroslag melting means for adding further droplets of molten metal into said molten metal pool.
 13. Apparatus as in claim 12 wherein said multiplicity of consumable electrodes are disposed in pairs at successive points along said trough, there being a pair of said nonconsumable electrodes adjacent each said pair of consumable electrodes. 